Presentation #401.01 in the session Numerics and Methods for Planetary Dynamics.
Asteroid families have been discovered by searching for clusters in proper orbital element space using the Hierarchical Clustering Method (HCM). However, this method is limited by the fact that some families overlap in that space. Because of this unavoidable limitation only about half the asteroids in the inner belt with absolute magnitude, H < 16.5 are recognized as belonging to distinct families. The remaining asteroids are currently designated as non-family. The number of distinct families has a direct bearing on the number of distinct sources of meteorites and near-Earth asteroids and our understanding of the origin and dynamical evolution of those bodies, and of the asteroid belt itself, is not complete without an understanding of the origin of the non-family asteroids. Here, we present a new method of searching for families that is supplementary to the HCM and has the potential of separating comparatively young families associated with compact clusters in orbital element space from old ghost families with dispersed orbital elements. This supplementary method is based on the idea that, because of orbital evolution due to Yarkovsky forces and other mechanisms, old ghost families should have lower number densities and be comparatively deficient in small asteroids. Hence, by mapping the asteroid number density in orbital element space and comparing that distribution with a map showing the distribution of the slopes of the size-frequency distributions (SFD), we can detect the likely locations of ghost families. Maps for the asteroids in the inner main belt are shown below. Asteroids in ghost families exist in those regions that have both a low number density and a low SFD slope. In the inner main belt, putative ghost families are found predominantly in the region of high orbital inclinations that is bounded by two major resonances. Results will be presented for other regions of the main belt.